In the related art, there has been known a damping force variable damper, which is capable of providing a required optimum damping force depending on a driving state when absorbing vibrations in order to improve steering stability and ride comfort in a vehicle.
The damping force is determined by the product of a damping coefficient and a stroke speed, but the stroke speed is uniquely determined in the driving state of the vehicle. Therefore, in the damping force variable damper, the damping force may be effectively varied by varying the damping coefficient. See, for example, JP2009-286233A (Reference 1) and JP05-104924A (Reference 2).
By the way, in an actual damping force variable damper, when the damping force is abruptly changed, the flow of oil rapidly varies in the damping force variable damper and an oil hammer occurs, which causes the generation of sound (impact sound).
In order to avoid this, it may be necessary to slowly vary the flow of oil in the damping force variable damper, that is, to slowly perform variation in damping force, but it may take time to achieve a target damping force and there is a risk of causing a deterioration in steering stability and a deterioration in ride comfort.
Thus, a need exists for a control apparatus of a damping force variable damper which is not susceptible to the drawback mentioned above.